1. Technical Field of the Invention
The present invention relates to novel photoprotective compositions comprising methyltrialkylsilanes containing a cinnamate, cinnamamide, benzalmalonamide or benzalmalonate function, the same being useful as sunscreens that are active in the field of UV radiation.
The present invention also relates to novel methyltrialkylsilanes containing a cinnamate, cinnamamide, benzalmalonamide or benzalmalonate function and to certain applications thereof.
2. Description of Background and/or Related and/or Prior Art
It is known that radiation with wavelengths ranging from 280 nm to 400 nm permits tanning of the human epidermis, and that radiation with wavelengths ranging from 280 to 320 nm, known as UV-B radiation, causes skin burns and erythema that may harm the development of a natural tan. For these reasons, and also for aesthetic reasons, there is an increasing demand for means for controlling this natural tanning. This UV-B radiation should thus be screened out.
It is also known that UV-A rays, with wavelengths ranging from 320 to 400 nm, which cause browning of the skin, are liable to induce impairment in the skin, especially in the case of sensitive skin and/or skin that is continually exposed to sunlight. UV-A rays in particular cause a loss of elasticity of the skin and the appearance of wrinkles, leading to premature aging of the skin. They promote the triggering of the erythemal reaction or amplify this reaction in the case of certain individuals and may even be the cause of phototoxic or photoallergic reactions. Thus, for aesthetic and cosmetic reasons such as conservation of the skin's natural elasticity, more and more individuals wish to control the effect of UV-A rays on their skin. It is thus desirable also to screen out UV-A radiation.
Many organic compounds intended for protecting the skin against UV-A and/or UV-B radiation have been proposed to date.
Most of these are aromatic compounds that absorb UV radiation in the region from 280 nm to 315 nm, or in the region from 315 nm to 400 nm and beyond, or even within both these regions. They are usually formulated in anti-sun or sunscreen compositions that are in the form of oil-in-water or water-in-oil emulsions. The organic screening agents, which are generally lipophilic or hydrophilic, are present in dissolved form, in one or other of these phases, in amounts that are suitable to obtain the desired sun protection factor (SPF).
The “sun protection factor” means the ratio of the irradiation time required to reach the erythema-forming threshold in the presence of the test screening agent, to the radiation time required to reach this same threshold in the absence of screening agent.
Besides their screening power on sunlight, photoprotective compounds must also have good cosmetic properties, good solubility in the usual solvents and in particular in fatty substances such as oils and fats, good resistance to water and to perspiration (remanence) and satisfactory photostability.
Among all of the aromatic compounds that have been recommended for this purpose, mention may be made especially of polysiloxane derivatives containing a benzalmalonate function, described in EP-A-358,584 and in EP-A-392,882 assigned to the assignee hereof. These compounds do indeed have good liposolubility. However, these substances contain very long silicone chains and, on account of their bulk, their synthesis and their incorporation into cosmetic compositions are laborious. Finally, their cosmetic properties are not always satisfactory.
In addition, mention may be made of the silane compounds containing benzalmalonate groups described in EP-A-2,868,905, which describes a process for improving the photostability of dibenzoylmethane derivatives with silane derivatives of benzalmalonates. Mention may also be made of the silane compounds containing benzalmalonate groups described in JP-07-330,779. In this case also, their solubilities in fatty substances and their cosmetic properties are not always satisfactory.